In recent years there has been a growing interest in increased automation in the control of the drive train of motor vehicles, and most especially in control of the drive train of large trucks. The use of automatic transmissions in passenger automobiles and light trucks is well known. The typical automatic transmission in such a vehicle employs a fluid torque converter and hydraulically actuated gears for selecting the final drive ratio between the engine shaft and the drive wheels. This gear selection is based upon engine speed, vehicle speed and the like. It is well known that such automatic transmissions reduce the effectiveness of the transmission of power from the engine to the drive shaft, with the consummate reduction in fuel economy and power as compared with the skilled operation of a manual transmission. Such hydraulic automatic transmissions have not achieved wide spread use in large motor trucks because of the reduction in efficiency of the operation of the vehicle.
One of the reasons for the loss of efficiency when employing a hydraulic automatic transmission is loss occurring in the fluid torque converter. A typical fluid torque converter exhibits slippage and consequent loss of torque and power in all modes. It is known in the art to provide lockup torque converters that provide a direct link between the input shaft and the output shaft of the transmission above certain engine speeds. This technique provides adequate torque transfer efficiency when engaged, however, this technique provides no gain in efficiency at lower speeds.
It has been proposed to eliminate the inefficiencies inherent in a hydraulic torque converter by substitution of an automatically actuated friction clutch. This substitution introduces another problem not exhibited in the use of the hydraulic torque converters. Friction clutches used exhibit considerable motion prior to initial clutch engagement. This point of initial clutch engagement is called the touch point. No substantial torque can be transferred through the clutch for clutch engagement before the touch point. The clutch controller preferably uses the touch point as the zero position for its control algorithm. Since no substantial controlled torque transfer can take place prior to the touch point, the clutch controller preferably rapidly advances the clutch to this point when controlling clutch engagement.
Thus it would be an advantage to provide automatic clutch actuation of a friction clutch that includes a reliable and automatic manner for determination of the clutch touch point. One proposal to satisfy this need is presented in the U.S. patent application Ser. No. 07/815,501 entitled TOUCH POINT IDENTIFICATION FOR AUTOMATIC CLUTCH CONTROLLER and assigned to the assignee of this invention. There the touch point is correctly identified but substantial time is required. The present invention is much faster, especially where the touch point history is known.